100 ° H. L. Hawkins—On Lovenia forbesi 
partly due to its exceptional smallness and perhaps also in part to 
the relative intractability of the Chalk it inhabits, but it must also 
be due in part to secondary calcification. It is clearly one, and 
apparently the first, of the group which includes Jf. castrum,' Bryd., 
and 2. pustulosa,* Bryd. ., and which is otherwise, except for a very 
brief interval at the base of the zone of B. mucronata, strictly 
unilaminate. 
EXPLANATION OF PLATE VI. 
(All figures magnified 12 diams.) 
Fie. : 
1, 2. Membranipora subacuminata. Zone of B. mucronata. Portsdown. 
3. M. Studlandensis. Zone of B. mucronata. Studland. 
4, M. Studlandensis. Another part of the same specimen showing broken 
ocecia. 
5. M. demissa. Zone of B. mucronata. Studland. 
6. M. Woodwardi, var. pinguescens. Trimingham. 
7. M. Woodwardt. Zone of M. cor-testudinarium. Seaford. 
8. Membraniporella pontifera. Zone of M. cor-anguinwm. Grea: 
0. M. obscwrata. Zone of M. cor-testudinarium. Seaford. 
(To be continued.) 
at 
If.—A REMARKABLE SrRucrure in Lovenra FORBESI FROM TILE 
re Miocene or Avsrratta. 
By H HERBERT L. HAWKINS, M.Sc., F.G.S:, Geological Department, Univer 
College, Reading. 
URING the preparation and arrangement of a series of Lovenia 
forbest from the Australian Miocene (presented to the Geological 
Department by Professor F. J. Cole), a peculiar interambulaeral 
structure was displayed. ‘lwo of the specimens are severely weathered, 
with the result that their surfaces are smooth (except for the areole 
of the large tubercles), while the sutures are clearly outlined in dark 
brown across the pale background of the plates. In this way there 
is revealed the surprising fact that plate-crushing and resorption, of 
a type similar to that often found in Echinoid ambulacra, occur in 
four of the interambulacral areas. There is no corresponding develop- 
ment in the ambulacra. iy. 
As far as I am aware, this peculiar condition has not been described 
‘previously in the species under notice, nor in any other Euechinoid, 
whether Regular or Irregular. Apart from its intrinsic interest, 
this apparently unique development throws much light upon the 
mechanism whereby the more usual ambulacral plate-crushing is 
produced. Hence a brief description of the specimens seems desirable ; 
and the description is followed by a discussion of the problem as 
solved by this new evidence. 
The following description is based solely on the two weathered 
specimens referred to above. They are registered in the Paleonto- 
logical Collection of University College, Reading, under the numbers 
546 A and B. Their dimensions (in millimetres) are as follows :— 
Ant.-Post. Diam. Transverse Diam. Height. 
i Nash Ye ie Rtn EL 20:8 112-9 
Jey 45 . 3 23:0 24-0 1. IL-2 
1 GEon. Mag., 1909, p. 398, Pl. XXII, Figs. 4, 5. 
2 GEOL. MAG., 1910, p. 488, Pl. XXXVI, Fig. 9. 
